Oxygen Myths: Why Bubbles Don’t Mean Breathable Water (And What Really Works)

[00:00:00] Welcome to this episode of the Aquarists Edge, a podcast for home aquarists just like you. Learn more about how to keep a thriving aquarium and discover ideas and tips to give your aquarium the edge. And now over to our host Arthur Preston. Welcome to this week's episode of the Aquarists Edge.

[00:00:22] Before I get into this week's episode topic, I want to invite all our South African listeners who will be heading to the Eastern Cape Aquatic Expo to come and say hi. I'm going to be there for all three days, that's May 30th to June 1st and I will be wearing an arts fishroom white golf shirt or hoodie and I would love to meet you face to face.

[00:00:46] I will be doing some interviews with some of the exhibitors and we'll put those onto other podcast episodes in the future. But it's always nice to see people face to face, to have a conversation, to share a passion for aquarium keeping and I'll be attending workshops and certainly making my way around the various exhibitors and chatting to folks as I go. So please do make a point if you see me, please come and find me, I would love to say hi.

[00:01:13] So that said, let's get into today's episode. To get us going, here's a question. When you see all those tiny bubbles rising from your sponge filter or your airstone, do you automatically think, perfect, that's oxygen for my fish? If you said yes, you're not alone, the vast majority of people would say that. But the reality is far more nuanced. In fact, those bubbles may be contributing very little to oxygenation

[00:01:40] and in some setups might even be doing more harm than good. In today's episode, we're going to look at how gas exchange works in an aquarium, why bubble size and behaviour matter more than quantity, how poorly designed filtration setups reduce oxygen availability, the role of surface agitation and water movement, the oxygen demands of different fish, and a couple of other hints and tips and tricks along the way. So let's get into it. Let's face it, bubbles look like oxygen.

[00:02:09] They fuel like oxygen. When you see those bubbles rising up in the tank, it's a very natural thing to go, well, my tank is being oxygenated. But what if I told you that most of the oxygen in your tank does not come from the bubbles themselves? Instead, it comes from gas exchange that happens right at the water's surface. When an airstone or sponge filter generates bubbles, they rise to the surface, but they don't dissolve significantly along the way. The larger the bubble, the less time it spends in the water column

[00:02:38] and the less gas it exchanges. Tiny micro bubbles stay suspended longer and they might seem more efficient, but if the surface of your tank is calm and glassy, you're missing the point entirely. Real gas exchange happens where water and air meet. That's where oxygen dissolves into the water and carbon dioxide escapes. If your tank has minimal surface agitation, the exchange rate will be low, no matter how many bubbles you have.

[00:03:06] And let's also not forget that excessive reliance on bubbles can also mask deeper issues. It's not just about oxygen, it's about circulation, the stratification of your water and how well your filtration integrates with the needs of your bio load. So let's get technical just for a moment. Oxygen enters your aquarium through a process known as diffusion. This happens when oxygen molecules move from the air, where they're abundant,

[00:03:34] into the water, where they are less so. This natural movement equalises the concentration. But water doesn't just passively accept oxygen. The rate of diffusion is affected by several factors, including surface area, surface agitation, temperature, senility and biological load. Let's look at each of those very briefly. A larger surface area allows for greater exchange. In terms of surface agitation,

[00:04:02] the movement of the water increases the contact between the water and the air. Temperature-wise, we know that warm water holds less oxygen. In terms of salinity, we also know that saltwater holds less oxygen than freshwater. And in terms of biological load, it's a fairly obvious connection. More fish and plants means that there's more demand for oxygen. And this is why a tank with strong surface agitation from a hang-on-back filter or powerhead may be far more oxygen-rich

[00:04:31] than a tank with a weak sponge filter producing a gentle bubble stream. Also remember, every tank has a unique oxygen budget. What works for a lightly stocked shrimp tank won't cut it for an African ciclid colony. Now, many hobbyists will opt for sponge filters. They're really great for biological filtration and they're easy to use. But their role in oxygenation is often misunderstood. I think of a lady by the name of Lisa who had a beautifully aquascaped 120-litre planted tank.

[00:05:01] She had two sponge filters in this tank. But her cherry barbs were always hanging out near the top. She thought they liked it there. But it actually turned out they were gasping for air. And she'd had her sponge filters for some time and they'd been producing micro bubbles that flowed straight up to the surface of the tank, but they barely made a ripple at the surface. Once she added a small surface skimmer and tilted her sponge filter tube slightly so that the bubbles broke the surface more aggressively, the fish started behaving normally within 24 hours.

[00:05:33] Another story I can share with you is a chap by the name of Andrew from Johannesburg. He had an overstocked 200-litre Oscar tank and he relied solely on a large sponge filter and a quiet air pump. But the surface looked like a still pond. After he lost power through a power outage, he lost three fish. Not from the build-up of toxins, but from oxygen deprivation. Now he uses dual power heads and a backup battery-operated air pump. Lesson learned.

[00:06:02] Here are some real improvements you can make to ensure that your tank is properly oxygenated. You can redirect your bubble flow. Position your uplift tube or air stone so that there's greater surface agitation. You could add a hang-on back filter or a surface skimmer. Both of these are excellent at increasing surface agitation. Using a power head will help circulate water and will mix oxygen-rich surface water into the lower levels of your tank. You could install a wave maker.

[00:06:29] That's great for very long tanks with potential dead zones. You could lower the water line slightly because this causes more splashing from your filter return which will increase the gas exchange. And don't forget to break up the films that you might find lying on your surface agitation. Things like oil slicks or protein films reduce oxygenation. So skim them or break them with added surface agitation. Think of oxygenation like an insurance policy. Redundancy is your friend, especially in high-stakes environments

[00:06:58] such as breeding tanks or species with a narrow tolerance range. If you notice that fish are gasping at the surface, that they seem to be lethargic or have a poor appetite. If you find them gathering around filter outlets or you notice slow growth or precaloration or even unexplained diorbs overnight, especially in planted tanks, it could well be that you have low oxygen in your tank. Be aware that oxygen levels often drop overnight due to plant respiration. If your fish are always gasping in the morning,

[00:07:29] consider adding greater nighttime aeration or if you have a CO2 injection system to reduce the CO2 during the evening. Also remember that different fish have different oxygen needs. Your labyrinth fish such as garamis or bettas, they breathe atmospheric air but they will still benefit from oxygen-rich water. Your bottom dwellers such as corridoras and loaches, you need to make sure that the circulation of oxygen-rich water reaches the substrate.

[00:07:58] Discus and angelfish come from slower, warmer waters but they are very sensitive to oxygen levels. Goldfish, especially your fancy breeds, need loads of oxygen. So you're going to want to use large filters and additional aeration in a goldfish tank. And don't forget your very active swimmers such as your danios and rainbow fish. They're oxygen-hungry by nature. Don't forget in your tanks you also have invertebrates. So bear in mind that shrimp are oxygen sensitive, especially in smaller nano tanks

[00:08:27] and that snails and crabs can suffer in dead zones without proper flow. So don't assume that one setup fits all. Match your oxygenation strategy to your livestock. It's interesting to note that seasonal changes can also impact oxygen in your tank. Temperature swings in summer can significantly lower dissolved oxygen. So even if your tank heat is off, the ambient temperature can push water into the 28 degrees Celsius plus. That's already compromising your oxygen levels.

[00:08:56] High humidity in the room can also play a role. When the air above the tank is saturated with moisture, the efficiency of oxygen transfer decreases slightly. It's not a major factor in every case, but in sealed rooms or fish rooms without ventilation it can add up. Winter heaters, while great for keeping things stable, also encourages stratification. That's a condition where the warm surface water becomes isolated from the cooler, denser bottom water. You're going to need to make sure there's circulation

[00:09:25] because otherwise you're going to have oxygen poor zones in your tank. Align your tank maintenance with seasonal changes and keep your oxygenation consistent and predictable. So that really helps us understand something about this myth that the more bubbles we have, the greater our oxygenation. That simply is not true. Filter bubbles can be misleading. It's the surface agitation that drives oxygenation. Poor filter placement and design can reduce oxygen availability.

[00:09:56] You need to understand your fish's oxygen needs and tailor your setup accordingly. Always test and observe. The bubbles may look pretty, but they won't tell you the whole story. And don't forget that environmental and seasonal conditions can affect your tank in more ways than you think. If this episode gave you a new perspective on the bubbles in your tank, I'd be so appreciative if you would subscribe to this podcast on your podcast app, if you would rate the podcast, share it with a fellow at-risk,

[00:10:24] and consider leaving a review on your podcast app such as your Apple Podcasts or Spotify. If you're watching or listening to this on YouTube, please go ahead and leave a comment, like it, subscribe to the channel. Next week my intention is to put out an Acris Edge podcast episode just before I go away on Friday. And I will consider putting out something during the actual expo next weekend. So folks, thanks for spending time with this topic today.

[00:10:52] Thanks for tuning in once again to the Acris Edge podcast. We have now passed 3000 downloads. We have well over a thousand regular listeners. I'm very grateful to all of you. Thank you so much for spending time, giving time to this podcast. And so until we meet again for the next episode, keep learning, keep discovering, and keep enjoying this amazing hobby. Bye for now. That's it for this episode of the Acris Edge.

[00:11:19] Please consider subscribing to this podcast so that you don't miss further episodes. We would love it if you would also rate and review the podcast as this helps make it visible to others. Until next time, keep learning and discovering, and keep finding your Acris Edge in this captivating and fascinating hobby.